The present invention relates to stabilized sighting systems comprising a stabilization mirror that is angularly steerable about two mutually orthogonal axes, in general an optical system for receiving incoming light beams in a single multispectral channel, with separation between spectrum bands being performed downstream by appropriate optical channels.
Numerous systems of this type are already known. Document U.S. Pat. No. 4,393,957 describes one such system, in which the stabilization mirror is:
steerable about a first or "lateral" axis PA1 onto equipment that is itself steerable about a second axis orthogonal to the first and intersecting it (often an elevation axis) PA1 onto an assembly that is steerable on a support about a third axis (a "circular" axis). PA1 a block comprising the catoptric optical system that is steerable over an angular range of about .+-.10.degree. about a lateral axis relative to internal equipment which is itself steerable relative to external equipment about an internal elevation axis that is orthogonal to the lateral axis; PA1 an external assembly that is steerable about a support around a circular axis which is parallel with or coincides with the lateral axis in a nominal position of the system, which external equipment may also include an external elevation axis parallel to the internal elevation axis, to support the inlet porthole and, depending on the mechanics, to make fine stabilization in elevation possible; PA1 a stabilization mirror accompanying the catoptric optical system in its rotary displacements with its displacement being reduced by half about the lateral axis; and PA1 servo-control means comprising a gyroscopic sensor tied to the block, having sensing axes parallel one with the lateral axis and the other with the internal elevation axis, control loops for the motors providing servo-control about the lateral axis and the internal elevation axis under the control of the output signals from the gyroscopic sensor, and loops for copying the position of the block by controlling the steering motors about the external elevation axis and about the circular axis. PA1 a small angular field provided by the telescope for use by imaging channels and by telemetry, laser designation, reconnaissance and/or identification channels; and PA1 one or more larger angular fields e.g. for use in imaging, watching, and detection functions.
A servo system, including a gyroscopic sensor connected to the mirror via angular laws described below, serves to control steering motors so as to stabilize the sighting direction, and also attempts to maintain the sighting line orthogonal to a plane containing the lateral axis and the elevation axis.
For stabilizing the sighting line during angular displacement of the support, by rotating the mirror, it is necessary to turn the mirror through an angle that is half the angle through which the support turns in the light propagation plane, and also through an angle of full amplitude in the plane perpendicular to the outlet light beam, while the inertia of the mirror tends to keep it in the same direction. In the more common systems, there is no optical element (other than one that is purely transparent) interposed between the sighted scene and the mirror. Consequently, the size of the mirror is equal at least to the inlet pupil, so its inertia is high. The high inertia reduces its frequency passband and makes it difficult to implement a servo system capable of compensating for disturbances of a vibratory nature at high frequency. In addition, the large size of the mirror makes it necessary to devote a large amount of volume to stabilizing servo-control means.